The advice given for sub woofer placement works. Just remember that as you move around the room looking for the sweet spot, your ears need to be at the height of the sub itself when it is placed. Remember also that you're not looking for the deepest bass, but the smoothest, non-boomy bass. This is where a $40 sound pressure meter from radio shack can really help. Just look for the pressure levels to maintain as near constant as you can get as the woofer plays a frequency sweep. Try to avoid locations that produce large spikes (corners) or drop-outs at certain frequencies.

I'm the camp that believes that better wiring equals better sound. I upgraded my wires from Monster flat cables to MIT Terminator bi-wire and the improvement in quality were not subtle. And yes, I did some blind testing with my family who were 5 for 5 in hearing the improvement. Your budget for wiring should be commiserate with the rest of your system. It doesn't make a lot of sense to spend $500 to wire speakers to a $400 receiver.